Benchmark oil for October delivery was down 31 cents to $106.09 per barrel at midday Bangkok time in electronic trading on the New York Mercantile Exchange. The contract fell $1.68 to close at $106.39 on Thursday.

President Barack Obama has threatened to launch military action against Syria for an alleged chemical weapons attack against civilians in suburban Damascus last month. But diplomats from Russia and the U.S. came up with a plan to induce Syria to give up its chemical weapons stockpile.

On Thursday, U.S. Secretary of State John Kerry called on the UN Security Council to back the U.S-Russia deal, which has reduced the threat of a U.S. military strike.

Fears of instability in the oil-rich Middle East were further allayed after reports signaled a return of more Libyan crude oil to the market. Production and exports have been sharply interrupted in the chaos following the overthrow of longtime dictator Moammar Gadhafi in 2011.

"There's been a bit of a step back in tensions in the Middle East," said Evan Lucas, market strategist at IG in Melbourne, Australia.

Brent crude, the benchmark for international crudes used by many U.S. refineries, fell 9 cents to $108.67 a barrel on the ICE Futures exchange in London.